Utility of FDG-PET/CT in Lymphoblastic Lymphoma

Abstract

Background: LBL is a rare, malignant disorder of precursor Tor Bcells, which forms the lymphoma variant of acute lymphoblastic leukemia (ALL). Whilst morphologically and immunophenotypically similar to ALL, distinction is made on degree of bone marrow infiltration (typically less than 25% in LBL). Due to the rarity of the condition, investigations at diagnosis, treatment approach and methods to evaluate disease response are not standardized. Bone marrow examination with MRD determination is the gold standard modality for disease monitoring in ALL yet the utility of this investigation is limited in LBL due to the low levels of marrow involvement at presentation. Computed tomography (CT) scanning is widely used in the diagnosis and assessment of lymphomas, however the criteria for disease are based purely on size of a lesion. Difficulties in distinguishing inflammatory from malignant lesions on CT have been widely reported (Elstrom et al. Blood. 2003;101(10):3875-6). 18FDG PET/CT has been shown to be sensitive for staging high grade non-Hodgkin’s lymphoma and is better at differentiating inflammatory from malignant lesions compared to CT alone (Ngeow et al, Ann Oncol. 2009;20(9):1543-7). Normalization of the SUV to a suitable reference region such as the tumorto-liver ratio (TLR), has reduced issues with inter-scanner variability. Retrospective data on the use of PET/CT in LBL is limited. In most series, few patients underwent PET/CT at diagnosis making interpretation of subsequent scans difficult thus PET/CT is currently only used at physician discretion in LBL.